1. Field of Invention
The present invention relates to an electro-optical device in which an electro-optical material such as a liquid crystal is enclosed between a substrate for an electro-optical device, such as a liquid crystal apparatus provided with a plurality of pixels formed in a matrix and an opposite substrate. More particularly, the present invention relates to an electro-optical device in which microlenses are formed on an opposite substrate, and a method for fabricating the same.
2. Description of Related Art
As shown in FIG. 11, a liquid crystal apparatus as an example of electro-optical devices substantially includes a liquid crystal apparatus substrate 30 provided with a pixel electrode 8 and a thin film transistor (hereinafter referred to as TFT) 10 for pixel-switching, an opposite substrate 20 provided with an opposite electrode 32, and a liquid crystal 39 as an electro-optical material enclosed and retained between the substrates. The liquid crystal apparatus substrate 30 and the opposite substrate 20 are adhered to each other with a given space therebetween by a sealing material 52 containing a gap material, and the liquid crystal 39 is enclosed in the space. Accordingly, in the liquid crystal apparatus substrate 30, by image signals applied to the pixel electrode 8 from a data line (not shown in the drawing) through the TFT 10, the alignment conditions of the liquid crystal 39 between the pixel electrode 8 and the opposite electrode 32 can be controlled. Therefore, in a transmissive liquid crystal apparatus, light incident on the side of the opposite substrate 20 is aligned into a predetermined linearly polarized light by an incident side polarizer (not shown in the drawing), and then enters the layer of the liquid crystal 39 from the side of the opposite substrate 20. The linearly polarized light passing through one region is emitted from the liquid crystal apparatus substrate 30 with the polarization axis of the transmitted light being twisted, while the linearly polarized light passing through another region is emitted from the liquid crystal apparatus substrate 30 with the polarization axis of the transmitted light not being twisted. Therefore, one of the linearly polarized light in which the polarization axis has been twisted by the liquid crystal 39 and the linearly polarized light in which the polarization axis has not been twisted passes through an outgoing side polarizer (not shown in the drawing). Thus, by controlling the polarization conditions in each pixel, predetermined information can be displayed.
When incident light from the opposite substrate 20 side enters a channel forming region (not shown in the drawing) of the TFT 10, a photoelectric current occurs in the region by a photoelectric conversion effect, resulting in a deterioration of transistor characteristics of the TFT 10. Therefore, generally, a light-shielding film 6 referred to as a black matrix or black mask composed of a metallic material such as chromium or a resin black is formed on the opposite substrate 20 at the position opposing each TFT 10. However, although the light-shielding film 6 must be formed widely in order to securely prevent light from entering the channel forming region of the TFT by means of the light-shielding film 6, if such a wide light-shielding film 6 is formed, the amount of light for display decreases. Even if the wide light-shielding film 6 is formed, oblique incident light cannot be shielded securely.
Such being the case, a structure in which microlenses L (small condenser lenses) are arrayed on the side of the opposite substrate 20 in the longitudinal direction has been invented. In such a structure, since incident light entering from the opposite substrate 20 side can be condensed toward each pixel electrode 8 by the respective microlenses L, even if the width of the light-shielding film 6 formed on the opposite substrate 20 side is narrow, or there is no light-shielding film 6 on the opposite substrate 20 side, light can be prevented from entering the channel forming region of the TFT 10. Thus, as the deterioration of transistor characteristics of the TFT 10 and the decrease in the amount of light for display can be prevented, reliable liquid crystal apparatuses which produce a bright display can be fabricated.
A method for fabricating such an opposite substrate 20 includes the steps of producing a lens array substrate LA in which a plurality of microlenses L are formed by etching the surface of a transparent substrate using a photolithographic technique, and then adhering a glass sheet 49 as a transparent cover to the lens array substrate LA by an adhesive 48. That is, in the conventional lens array substrate LA, since the entire region is etched excluding a portion in which microlenses L are formed, a peripheral region LB of the region in which microlenses L are formed is also etched, the peripheral region LB being lower in height comparison with the microlenses L. With respect to the opposite substrate 20, an opposite electrode 32 and a light-shielding film 6 are formed, in that order, on the surface of the glass sheet 49 adhered to the lens array substrate LA, and then, a polyimide resin 47 is applied thinly thereon and thermally cured at temperatures of approximately 150 to 200° C., followed by rubbing. With respect to the liquid crystal apparatus substrate 30, after the TFT 10 and the pixel electrode 8 are formed, in that order, a polyimide resin 46 is applied thinly thereon and thermally cured at temperatures of approximately 150 to 200° C., followed by rubbing. Then, after a sealing material 52 containing a gap material is applied to the surface of the liquid crystal apparatus substrate 30 in the region which overlaps the peripheral region LB of the opposite substrate 20, the opposite substrate 20 and the liquid crystal apparatus substrate 30 are adhered together with the sealing material 52. The step of adhering the opposite substrate 20 and the liquid crystal apparatus substrate 30 together is important in determining a space between the substrates. Generally, the sealing material 52 is preliminarily cured by emitting light on the sealing material 52 from the side of the opposite substrate 20 while the opposite substrate 20 is being pressed to the liquid crystal apparatus substrate 30 to secure a given space between the opposite substrate 20 and the liquid crystal apparatus substrate 30, and then the sealing material 52 is post-cured.
In the known lens array substrate LA, however, since the peripheral region LB in the region in which microlenses L are formed is lower in height in comparison with the microlenses L, various adverse effects are caused because the cover (glass sheet) 49 is adhered to the lens array substrate LA with a significantly thick adhesive 48. For example, when the opposite substrate 20 and the liquid crystal apparatus substrate 30 are adhered together with the sealing material 52, even if the opposite substrate 20 is pressed to the liquid crystal apparatus substrate 30, the thick adhesive 48 functions as a cushion in the peripheral region LB, and thus, a space (cell gap) between the opposite substrate 20 and the liquid crystal apparatus substrate 30 cannot be controlled. As a result, display quality deteriorates in the liquid crystal apparatus.
Also, with respect to the fabrication of the opposite substrate 20, if the adhesive 48 in the peripheral region LB is thick when the polyimide resin 47 as an alignment layer is thermally cured, warpage, waviness, or the like may occur in the opposite substrate 20 because of stress due to the adhesive 48. In such a case, the space between the opposite substrate 20 and the liquid crystal apparatus substrate 30 cannot be controlled, resulting in a deterioration of display quality in the liquid crystal apparatus.